In the fabrication of microlithographic patterns, for use, as examples, in photoetching processes (e.g. processing semiconductor integrated circuits and in production of electronic circuits) there is a continuing need to improve photoresist materials in order to create and to replicate high-density information patterns on semiconductor bodies and other substrates. Properties of increasingly high resolution, fast and faithful response to control energy whether in the form of a plasma, an electron beam, heat energy, visible light, or other, are all desired.
Chalcogenide glass films, such as Se-Ge glasses, As.sub.2 S.sub.3 glasses or other binary glassy compounds of oxygen, sulfur, selenium and tellurium, have been found to exhibit a selective etching effect due to photoexposure such that they are suitable for use as photoresist materials. Being glass, i.e., amorphous in structure, they exhibit also high resoltion capabilities suitable for microlithographic applications (Nagai, et al, "New application of Se-Ge glasses to silicon micro-fabrication technology," Applied Physics Letter, Vol. 28, No. 3, Feb. 1 1976, pages 145-147).
It is known that a thin (less than 100 Angstrom units) layer of metallic silver on a chalcogenide glass acts to "photodope" the glass, as the silver can be driven into the glass to improve the photoresist properties. When silver is in the chalcogenide glass in patterns, there is differential resistance to etching compositions. (Yoshikawa, et al, "A novel inorganic photoresist utilizing Ag photodoping in Se-Ge glass films," Applied Physics Letters, Vol. 29, No. 10, Nov. 15 1976, pages 677-679). The same effects of photodoping were later observed in electron-beam irradiation (Yoshikawa, et al. "A new inorganic electron resist of high contrast," Applied Physics Letters, Vol. 31, No. 3, Aug. 1 1977, pages 161-163). Electron irradiation on a double-layered film of Ag and Se-Ge glass, like irradiation with light, gives rise to driving silver into the underlying Se-Ge layer.
When silver is forced into a chalcogenide glass in patterns for etching, the silver-doped chalcogenide becomes insoluble in alkaline solutions. It has been suggested that silver halide can be used in place of silver to supply the silver for photodoping through dissociation into metallic silver and halogen gases upon irradiation, and a 20 nm thick layer of AgCl deposited from vapor on a glass film of As.sub.2 S.sub.3 and 300 nm thick has been reported to be useful for photodoping, but its sensitivity, or photographic speed is still slower than desired (Kolwicz and Chang "Silver Halide-Chalcogenide Glass Inorganic Resists for X-Ray Lithography"- unpublished).
When Se-Ge glass is etched after conventional photoexposure the result is a photographically positive photoresist, or a resist in which the exposed areas of the glass are etched away. At least one report states that the opposite is true of an As.sub.2 S.sub.3 glass where conventional photoexposure and etching yield a negative resist (Kolwicz and Chang, supra). However, when the glass is "photodoped" and silver is driven into the glass by a pattern of actinic radiation, both the Se-Ge glass and the As.sub.2 S.sub.3 glass form a negative resist. (Yoshikawa, et. al., Applied Physics Letters, Vol. 29, No. 10, pages 677-679).